'\" et
.TH SETVBUF "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
setvbuf
\(em assign buffering to a stream
.SH SYNOPSIS
.LP
.nf
#include <stdio.h>
.P
int setvbuf(FILE *restrict \fIstream\fP, char *restrict \fIbuf\fP, int \fItype\fP,
    size_t \fIsize\fP);
.fi
.SH DESCRIPTION
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
The
\fIsetvbuf\fR()
function may be used after the stream pointed to by
.IR stream
is associated with an open file but before any other operation
(other than an unsuccessful call to
\fIsetvbuf\fR())
is performed on the stream. The argument
.IR type
determines how
.IR stream
shall be buffered, as follows:
.IP " *" 4
{_IOFBF} shall cause input/output to be fully buffered.
.IP " *" 4
{_IOLBF} shall cause input/output to be line buffered.
.IP " *" 4
{_IONBF} shall cause input/output to be unbuffered.
.P
If
.IR buf
is not a null pointer, the array it points to may be used instead of a
buffer allocated by
\fIsetvbuf\fR()
and the argument
.IR size
specifies the size of the array; otherwise,
.IR size
may determine the size of a buffer allocated by the
\fIsetvbuf\fR()
function. The contents of the array at any time are unspecified.
.P
For information about streams, see
.IR "Section 2.5" ", " "Standard I/O Streams".
.SH "RETURN VALUE"
Upon successful completion,
\fIsetvbuf\fR()
shall return 0. Otherwise, it shall return a non-zero value if an
invalid value is given for
.IR type
or if the request cannot be honored,
and may set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIsetvbuf\fR()
function may fail if:
.TP
.BR EBADF
The file descriptor underlying
.IR stream
is not valid.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
A common source of error is allocating buffer space as an ``automatic''
variable in a code block, and then failing to close the stream in the
same block.
.P
With
\fIsetvbuf\fR(),
allocating a buffer of
.IR size
bytes does not necessarily imply that all of
.IR size
bytes are used for the buffer area.
.P
Applications should note that many implementations only provide line
buffering on input from terminal devices.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.5" ", " "Standard I/O Streams",
.IR "\fIfopen\fR\^(\|)",
.IR "\fIsetbuf\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<stdio.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
